1. Field of the Invention
This invention relates to polyamic acid, and an electrode having an active layer made from the polyamic acid, in which the polyamic acid is used to detect hydrogen peroxide.
2. Description of the Related Art
Hydrogen peroxide (H2O2) is a reactive oxygen species and a byproduct of several types of oxidative metabolism. Because the accurate determination of H2O2 is of practical importance in the clinical, environmental and industrial fields, increasing interest has focused on fabrication of reliable H2O2 biosensors. Due to their high selectivity and sensitivity, electrochemical devices have been used extensively to detect H2O2.
In electrochemical devices, electrodes used to detect analytes are either enzyme-based or enzyme-free electrodes. Enzyme-free electrodes can be made by forming an active layer on a conductor. The materials for the active layer can be inorganic materials (i.e., metallic nano-particles, metallic oxides, transition metals, carbon nanotubes, etc.), organic materials (i.e., polyamic acid, polyaniline, poly(aniline-co-p-aminophenol)) or organic-inorganic materials (i.e., polyaniline-carbon nanotubes).
As to an electrochemical device using the enzyme-free electrode, an oxidation potential (approximately 0.5 V to 0.7 V) is usually measured in this device to determine the amount of hydrogen peroxide. Since the oxidation potential is susceptible to interference with other undesired substances, such as uric acid (UA) and ascorbic acid (AA), in a test sample, the specificity for hydrogen peroxide is reduced and the accuracy of the test result would be adversely affected. Therefore, improvements for the electrodes of the electrochemical devices are aimed at detecting H2O2 at low potential while eliminating the interference of interfering molecules.
An imine group of an aromatic ring (such as pyridine) can be oxidized by H2O2 in an aqueous acetic acid solution to form N-oxide (see the following reaction formula). Therefore, electrodes that are made from materials modified with imidazole, thiazole, or oxazole are suitable to detect H2O2 or peroxy acid in the presence of acetic acid.

The inventors of the present invention have disclosed using poly (N-butyl benzimidazole)-modified gold electrode for the detection of hydrogen peroxide [Analytica Chimica Acta 2011, 693, 114-120]. The modified electrode detects hydrogen peroxide in the presence of carboxylic acid. The modified electrode has a detection range of 12.5 μM˜5.0 mM, with a sensitivity of 419.4 μA/mM·cm2, and response time of 6.3 seconds.
Accordingly, the detection of hydrogen peroxide using an electrochemical device would be ideal when the detection thereof occurs at low potential or under reduction potential without electrochemical reaction of other undesired analytes. In addition, the electrochemical device should have a short response time and high sensitivity.